Low noise traveling wave tubes



Oct. 13, 1959 Filed April 11l 1951 C. F. QUATE LOW NOISE TRAVELING WAVE TUBES 4 Sheets-Sheet 1 A VE coND/ T/oNs AT POINT b F/a/c L@ En,

NO/SE SIGNAL ATTORNEY @et B, i959 c. F. QUATE 2,908,844

LOW NOISE TRAVELING WAVE TUBES FiledApril 11. 1951 4 Sheets-Sheet 2 .N D lk DO 6R.

/N/ENTO'? C. F.' QUATE BV ATTORNEY c. F. QUA-rE 2,908,844

4 Sheets-Sheet 3 LOW NOISE TRAVELING WAVE TUBES Oct. 13, 1959 Filed April 11. 1915i ELECTRON FLOW /NVENTOR C. E' QUA 7 E BV Arrow/vnv DIELEC TR/C (HI nnnnf).

- te` trewehng'1waivetubing4 nii United States., Patent i 2,908,844 Low Nolsnrmvnizm@ WnvE-f Calvin Quatefliexgkeley IK-'Ieiglrltsr assi-guur tollel Tel'ephonLaboratoi-ies, orporated, New York, N.Y., a cofpo'a'tidn ef NewYork c @pincet-ien: Aspirin, issn, Serienr Ndizzbne 2s C'l'iins. (ci. 315-316) ngradio ati veinei 2,938,844 Peiterifd Get; 1'3, i959"V 2 i'tcitirr into'V the reigic'n'l of interaction With the electric field".v In' practice' it hasV` been' found fhat'hthe electron str for' purposes of analysis; aS

more particularly; td` n'iiiiini` 1 noise ini'their dperia'tidn restil'tng rr each case' freni the norhiigne'tjf o the efecton sfreari.

er titi-Velin@` Ywaive'interneticnin aj traveling weve; tnbe chewsI that tneiprepngetien characteristics ef tvelin Wave wflileilfil'lV cumulative; interaction' with theeletron sfeznr can't b'eprslented By' four natur'a'l n'iodes3 df propagation trl-birgtheL electric circuit and elecstrearn- Of these, three are forwardk traveling eL backward traveling'wave; If

ravehng waves Whlch have the characteristics set fr leeihaliove as" characteristic' of those set up" by tiireirgiirin' ciiiniritive interaction te theV beginning cf diecella't'io'r'iv section. Theng since cuniulative intere action 'is' there inhiited, the three waveswill travelfas o'rdil'giryn w'aves al'ngY the' electric circuit and hence can convenientlS/h'e represented by the composite wave which is their vector sum and which will travel therethrough and be attenuated in accordance with the attenuation characteristics of this Section. However, at the beginning of the main section where cumulative interaction again results, this composite wave will act in themanner of a signal input wave applied thereto and will accordingly set up three forward waves, in the manner characteristic of cumulative interaction. Additionally, at the origin of the main section, the noise components there in the electron stream have the effect of setting up three additional forward traveling waves. In the practice of the present invention, the tube characteristics are chosen to provide -at the start of the main section cancellation between the increasing wave component set up by the noise wave which has traversed the preliminary and intermediate sections `and the increasing wave component of the new noise wave set up originally at this point by the noise fluctuations in the electron stream. In particular, the attenuation and phase shift characteristics of the cancellation section are chosen to make these two increasing waves equal in magnitude but opposite in phase. More particularly, the desired phase shift characteristics of the cancellation section are achieved by making the electrical length of the section relative to the increasing wave component of the noise wave different from the electrical length of the section relative to the noise fluctuations on the electron stream. It will be seen that, because of the dissimilarities in the manner of injection between the signal and noise waves, the condition for noise cancellation will not at the same time seriously affect the amplification of the signal. By suppression of the increasing wave of the noise components in this way at the commencement of the main section of the circuit, and by making the main section of suicient length so that the other waves of the noise components become unimportant, relatively noise-free operation can be achieved over a considerable range of frequencies.

By way of example, the invention will be described with particular reference to a noise cancellation arrangement for a helix-type traveling wave tube, although as already pointed out hereinabove the invention can be adapted to provide noise cancellation in other tube types which utilize the cumulative interaction between an electron stream and an electromagnetic wave.

In the helix-type tube as known hitherto, the wave transmission circuit comprises a helix continuously and uniformly wound to a pitch which produces a slow wave having an axial velocity in the direction of the electron stream suitable for producing cumulative interaction between the stream and the slow wave. In the practice of the present invention, the helix circuit comprises a preliminary and a main section, uniformly wound to the necessary pitch and properly positioned in the path of the electron stream so that cumulative interaction results, and a cancellation section intermediate therewith wherein cumulative interaction is inhibited. A preferred embodiment utilizes a cancellation section in which the helix is wound to a pitch which results in the velocity of the traveling wave in the direction of the electron beam being sufficiently dissimilar to the velocity of the electron stream that there is substantially no cumulative interaction therebetween. The characteristics of this section are chosen to provide the cancellation effects described.

The invention will be better understood with reference to the following more detailed description taken in connection with the accompanying drawings forming a part thereof, in which:

Fig. 1 shows schematically an electric circuit of a kind which can be used in the practice of the invention; Figs. 1A through 1E are a series of vector diagrams illustrating at the designated points of the circuit of Fig. 1 the relative magnitude and phase of the noise wave components characteristic of traveling wave tube operation; and

.4 Figs. 1F, 1G, 1H, 1I and 1K, respectively show the corresponding components of a signal Wave;

Figs. 2 and 3 show, in schematic form, respectively, a traveling wave tube and a magnetron amplifier in each of which there is incorporated a helix-type circuit which has been modified for the practice of the invention;

Figs. 4A through 4D show, in schematic form, various modifications possible with helix-type circuits to inhibit cumulative interaction between the electromagnetic wave and the electron stream for the practice of the invention;

Fig. 5 shows in schematic form a filter type traveling wave tube which can be adapted for the practice of the invention; and

Figs. 6A through 6D show various modifications possible for adapting a filter type circuit for the practice of the invention.

Before describing specifically illustrative embodiments o f the invention, it will be helpful first to analyze in a qualitative sense the principles underlying the invention. In this analysis reference will be made to Fig. 1 and its associated vector diagrams, Figs. 1A to 1K, inclusive.

The circuit 10, which for purposes of exposition is shown as a helix, comprises a preliminary section 11 which is adapted to provide cumulative interaction between the traveling wave and the electron stream, an intermediate cancellation section 12 which is adapted to inhibit cumulative interaction so that it serves as a drift section, and a main section 13 which is also adapted for cumulative interaction. An electron gun (not shown in Fig. 1 but shown in Figs. 2 and 3) provides an electron stream which flows parallel to the axis of the helix in coupled relation therewith. For traveling wave tube operation, the circuit is immersed in a longitudinal magnetic field. In such an arrangement, the total electric field is composed of two parts; one is associated with carrying radio frequency power along the circuit and is strong near the circuit and the other part results from local space charge within the beam and is strong near the beam.

In the more quantitative analysis which will be set forth with reference to Fig. 2, both fields are accounted for, but in the qualitative discussion which follows here, it will be sufficient to discuss only the power carrying component of the field. At the input to the circuit 10, point a, there is a certain noise velocity vna and a given noise current qna (the noise current and velocity being entirely correlated with one another). Due to the noise current and velocity, there are excited on the circuit three noise components of electric field as illustrated in Fig. 1A. Here Ela represents the field component of Ithe increasing Wave, EML the field component of the decreasing wave, and Ega the field component of the unattenuated wave. Since the resultant noise eld at point a is zero, the three waves are necessarily out of phase. Moving down the electric circuit at the direct-current velocity of the electron stream, the three electric field vectors rotate in phase and change in magnitude. At point b between the preliminary section 11 and cancellation section 12, the three components will be as shown 'in Fig. 1B. Since section 12 acts as a drift section,

the three waves designated Elb, Ezb, and Eab, corresponding to the waves Ela, Ega, E33, respectively, can be represented by their sum at that point ETb. This wave will be propagated through section 12, being attenuated by the factor a, and having its phase shifted through the angle 03 with respect to a frame of reference moving with electron stream. Therefore, at point c, which is the end of section 12 and the start of the main section 13, the electric field ETc resulting from the noise wave set up at point a will be given by the expression the electric field ETc may be represented as the three Waves Ele, Ezc, and 133e, as shown in Fig. 1C, in phase with the` field ETC. Additionally, atpoint-A the noise current qm, and noise velocity vx,c in the electron stream there set up three additional waves Em, Ecz, and ES, of which the first is. they increasing wave, the second the decreasing wave and lthe third is the unatteunated wave.

the noise current and velocity: in-thevstreanr as shown in f Fig, 1E. In practice, inorder to realize cancellation it may also be necessary to adjust parameters characteristic of the electron gun and preliminary region of the electric circuit. This willi be made evident in the quantitative analysis to follow.` Finally, it is. import-antto make the length of the main section 13 beyond the point c of suicient length so that only the single increasing wave is of importance.

The vector diagrams of Figs. 1F through 1K correspond respectively, to the diag-rams of Figs. 1A .through 1E which are used to illustrate that noise cancellation can be efected without' appreciablev disturbance of the ampl'i'- cation of the input signal. The basic factor that makes noise cancellation independentl of signal amplification is the dissirnilarity in input boundary conditions between the noise and. signal waves. At point a, the electric field resulting from .the signalwave is. necessarily equal thereto While signalvelocity. and' current' components have not yet been setup inthe electron stream'.l isin. contrast with the input. noise conditions which include noise velocity andA current components inthe electron `stream but no noise field'; Consequently, it can' be appreciated that ordinarily the" signal field andthe' signalvelocit'yandcurrent components in the stream at point c willbe unrelated to :the corresponding noise components. Accordingly, since a point of cancellation: for' a given electric circuit can only occur for particular relationships*between-` the several input components ofA electric field, if this point is chosen to cancel the noise, itfwilllnot ordinarily cancel the signal. v

Itmay be convenient to think of the preliminary section and intermediate noise cancellation section as integral parts of the electron. gun stream source independent of the input signal source: sinceiit is possible to insert the input signal wave at a pointfurther along in the electric circuit, as, for example,.atfthefstart of the main section. However, when the input signal is inserted at a point other than the input end ofthe'electric circuit, measures should be taken to insure that. this signal will be propagated through the circuit only in the direction of electron stream ow.

It can be appreciatedthatthese principles of noise cancellation are; applicable to other devices", as,.for example the magnetron amplifier, which. similarly utilizes vthe cumulative interaction between an electron stream and an electromagnetic wave. It is characteristic of such `devices that cumulative. interaction may be represented as setting up a plurality of waves at the origin of such interaction. In the magnetronA ampli-tier, there are setup two principal wavesA of.V which. one is..an increasingwaveinthe manner of. the traveling wave tube. To reduce the effect of noise variations in the electron stream in these devices, therer can be obtained cancellation of this increasing wave in accordance twit-h f the principlesv set fortli for thetraveling. wave tube.

FigwZ shows, in schematic form, ahelixztype traveling wave tube in which there is' incorporatedlfa noisel cancellation section of the kind described with reference to Fig. 1`. The'travelingwave tube 100)utilizesja.-sl'ozwwaveeelectrie interaction circuit 10 along which is' transmitted an electromagnetic wave supplied Ifrom an input source at point ai at. the'A inp'ut ornpstreanr end of the circuit. t will be convenientto userthe terms iupstream and down-i stream to denote relative separation from the electron source. electron gun structure 20 positioned beyond the input errdY ofthe circuitprojects an electron stream therethrough paralleli to the circuit axis and inthe direction of wave propagation. The electronv gunv is/ characterized by adirect-current: transit angle- 01 between its cathode 21 and anode 22. The anode 22 is separated from the input end of thecircuit, point a, by a directcurrent transit angle 02. At the opposite end of the electric circuit, the electromagnetic wave is supplied to an output Wave circuit for utilization. Beyond the output end of the electric circuit, there is positioned a collector anode 17 in target relation to the electron stream source. To insure alignment of the electron flow, the solenoid 25 provides the longitudinal magnet Iield B.

As is well known, if the electron velocity supplied:V by the electron stream source is adjusted to be substantially the same as the wave velocity inthe`v electric circuitai'n the absence of the electron stream; tli'e presencel of and interaction withY the electron stream produces amplification of the electromagnetic wave propagatedv in the electric circuit in the direction of electron motion. In helixtype travelingfwave' tubesknowni hitherto, the electric interaction circuit has comprised a helix which,- with'- the possible exception of' modications at`= the terminals for broad-band matching purposes, as, for example, tapering the pitch, has been substantially uniformly and continuously `wound-to` apitch which sought to achieve cumulative interaction-between thelelectron strearn-andA the travcling. electromagnetic Wave along the entire length of-the helix. Howeveryinf accordance with the invention,y the electric circuit shown ink the tube ofY Fig. 2 as discussed with reference to Fig. 1, comprises a relatively short preliminary amplifier section-111: and a relatively longer main amplifier section 13 in which the helix is 4uniformly wound to provide cumulative interaction therealong, and a relatively shorter intermediate cancellation' section 12 connected therebetween from point b to point cV in which the uniformity of the helix is changed'suificiently so that there is no cumulative interaction between the electron stream and-the traveling wave. Such an interactioncircuit can be describedas one having a relatively short preliminary section 11 and a relatively long main section 13 of bothof which the` retardation characteristicissuited for cumulative interactionbetweenfthetraveling .wave and' stream and a relatively sliort" intennediate section 12 where the retardation characteristic is unsuited for cumulative interaction between-the traveling wave and stream. This uniformity can be changed either by varying the pitch to disturb the synchronization between the traveling wave and electron stream necessary for cumulative interaction and/or by displacement ofI this section of the helix to negative coupling between the stream and traveling wave. It is a characteristic'of'such an electric circuit' that by suitable positioning and design, this intermediate section ca'nbe utilizedto effect substantial' cancellation of spurious noise lcomponents inthe traveling wave' arising from noise. iluctuations in theelectron stream; More particularly', if the electrical length ofi the' wave propagation circuitin the cancellation or intermediate section isv made to dif-r fer from the' electrical length of the' stream path in the cancellation section by a sucient amount, the noise cornponents of the wave oir-the Wave propagation circuit will be approximately out of phase with the noise wave induced on the main secti'rnby". the electron stream and substantial cancellation of the noise wave results.

It m-ay be helpful to analyze the noise cancellation scheme of the'-.pres`ent invent-iodina more' quantitative fashion for the `case of a traveling wave tube of thev kind" illustrated in Fig. 2. The theoretical noise figure fora conventional. travelingffvvavev tube has, already been. evaluated for the case where the space chargefefectsmayfbe ignored in the region beyond the anode of the electron gun of the stream source by I. R. Pierceand is set forth i on pages 145-156 of his book entitled Traveling Wave Tubes, published in 1950 by D. Van Nostrand Company, Inc., New York.

In the present lanalysis the space charge eeet will be considered, although partition eifects introduced by the tube elements will be ignored, and so the analysis is begun with the expressions obtained by Pierce (supra) for the noise current and velocity at the anode, namely Equations l and 2 express the input boundary conditions for the drift region between the anode of the gun and t-he input of the electric circuit. In such a drift region the alternating current phenomena is characterized by two space charge waves which propagate as ejwt-jziz where 4QC3=the space charge parameter of the beam deined by Pierce (supra) z=the distance along the circuit in the direction of electron llow The electric eld associated with each of the space charge waves has been evaluated in terms of the velocity and current as expressed by the relations With Equations 5 and 6 the electric iield set up in each wave by the input boundary conditions of Equations 1 and 2 can be readily obtained. Equation 4 then expresses the manner in which the eld propagates along the beam. With the value of the electric eld at the output of the rst drift region there can be utilized Equations 5 and 6 to nd the noise current and velocity at the input to the circuit, point a of Fig. 2, and they can be written as 02=directcurrent transit angle from the anode to the Circuit input point a y8 With the input boundary conditionsY of Equations` 7 and 8 the three Waves set up on the circuit can be written for the velocity Where CD=(5152)(51*'33)(5r-53) (13) Incidentally, it should be pointed out that originally Pierce defined n: (xn+jyu)c but later changed to the notation employed here where with corresponding expressions for qza and qga. Also with corresponding expressions for E23, and Esa.

Now again note that Ela represents the total eld associated with the amplified wave and, as is described in an article by J. R. Pierce, entitled Effect of Passive Modes in TW Tubes, Proceedings of Institute of Radio Engineers, volume 36, pages 993 through 997 (1948), the relation between En, and the power carrying cornponent, E1n, is

E1 E1n p (1+4QC(.7`51)) Now at point b, the input to the cancellation section with corresponding expression for qzb and qgb.

There can be written for the total components at point b l0 1 1) qw] o C o.D.

UFOD.

and

. Now therecan.. beicomputed the noise. velocity vc and current qcC at point c at the output of the. cancellation sectiontresulting; from, the. noise` components, v1,` and qu.VV

tr point? b? there-` can bewritten for the. eldsassociated'with thelt'wo space charge waves.

auch at pointt c where, ci is less than. unity and representsthe attenua-` tionjetween. b" and c and H3 is the phase shift, of the Wave. with .respect to a `wave. traveling. at. the. velocity: oflthe electronstream.

`Wi`th vc,` qc and. Ep: determined, there, can be derived an l`expressliorr-for the` field` excited. on. helix in the, i11-y creasingwavet.

cancellation. scheme` resolves into adjusting the pertinent parameters suchthat Einp=0l Or (5a-P53) +DA1(52-4QCI) -l-Fa=0 (3@ This condition will resultY inl a.r noise'gure oli zero decibels providedf the conditions expressed. by Equation 36% do: not-v at` theV same time cancel thev incoming radio frequency sign-alf. By calculationsl similar to those just carriedf out, it can be-V shown.l that.: Equation 36; docs: not express the condition for signal-v cancellation.

Iny Fig. 3^V there is` shown schematically a magnetron amplierr200 in whichthereis: incorporated an: electric circuit- 10 of` the kindel `described before with reference to Figi l. The electron: streami which issupplied from the cathode 121 of the'gun 120 has initially a component i'na direction, perpendicular t'or the directionoi travel of the electromagnetic waves setup by*k the: electric cir; cuit but itis.` bent to the', desired direction along thaof wave: propagation byV means of ae magneticA ielrl: Bim, not illustrated, whichr isztransverseboth tofthe wave propaga tion direction and?. tot the'directcurrent electric el set up between the cathode 121 and electrode 122 and the electricY circuiti 10: For as. moredetailed description. of this and other forms. oh magnetron, amplfers. refer@ ence is made to they second-mentionedV Piercef` applica? tion. The principles of theinvention, however, are little affected v byY thel differences bet-Ween l the ma gnetron amplilier landV traveling; wave' tube amplifier.` As with: the traveling wave tube, there is-v set up inthev main; section 13 by the noise iiuctuations of' they electron stream', a noise. Wave which includes an; increasing; component. In accordance with the-invention; by. means of the preliminary section 11 and the intermediate'cancellation section 12, there is setup in themain: section anotherV noise waveV of. which thel increasing component is a waveV equal in magnitude and opposite inv phase to that of thev other increasing wave whereby substantial. reduction ofthe effect` of noise fluctuations inf the.v electron stream: is realized, in the same manner describedk aboveirr detail for the traveling wave tube ampliiier.`

It can be appreciated that` therearev numerous techniques which maybeV adaptedfor inhibiting'` the; cumulaf t-ive interaction between the electr-om stream and thee1ectromagneticwaa/e, forV setting up: asecondcancellingfwave and` makingn possible thereby the` practice of the present invention. In. apreferred` embodiment, this effect4 is realizedfbychanging the aXialvelocity of. wa-ve propagation. (i-.e. retard-ation characteristic)l i-n: anu intermediate regionotthe circuit. This, cannbe done easilyy by: modif iications of t-he circuit geometry in the region` affected'.-I One instance-.of` this technique has beernused in; thefarrangemen't, of Eig.: 2 in which. the pitch of the heliiais. changedl in` the cancel-lation` section to; vary the` axial wave velocity. Additionally, the axial wave velocity' can-'be changedin-a particular regionV by val'y-inglthel dielectric surrounding the circuit in` that region. C on- Where Novia equation sa there is expfessedithe eenige@ upaby'inereasing waveon the lieliieoutputlseetionr The versely,A cumulative interaction can. be inhibited .hy modifying` the average velocity of. the. electron. stream in a particular region. Still another method is toV displace the cancellation. portionv of the` electric; circuit sufficiently to remove its ielfd from the region ofeffective cou-.` pling with the electron stream. However, it is portant that the arrangement. employed permit good matching between the several sections of the circuit so that reilections in the circuit are avoided.

The techniques described briey above are all'susceptible of` many possible. embodiments, depending.v on the type of-ramplifiierandi Wave circuit employed'l. However, the sameprinciplesfare generally applicable, regardless of@ the particular form ofelectric circuit employed typeof cumulative interaction operation utilized. It may be helpful to describe with some particularity, by way of illustration, a few representative embodiments, although it can be appreciated that a much larger variety is possible.

For the helix type electric circuit, the geometry may be changed in several ways to vary the axial velocity of wave propagation therethrough. As an alternative to changing the pitch with which the helix is wound as described hereinabove with reference to Fig. 2, the same result may be had by changing the radius and keeping the pitch uniform. In Fig. 4A there is shown a helix circuit 30 which comprises a preliminary section 31 and a main section 32 of a first radius and an intermediate cancellation section 33 of a larger radius to produce a decrease in axial wave velocity therethrough.

In Fig. 4B, there is shown a helix circuit 40 in which the intermediate cancellation section 42 has been displaced with respect to the preliminary section 41, the main section 43, and electron stream 44 to eliminate coupling with the stream. Within this section, the helix could be wound with various combinations of pitches and radii.

In Fig. 4C, there is shown a circuit 50 which is a variation of the circuit 40 of Fig. 4B. In this case, the beam within the cancellation section 52 between the preliminary section 51 and the main section 53 is surrounded by a conducting cylinder 54. By providing a difference in direct-current potential between the cylinder and the circuit, the average velocity of the electron stream can be changed in the region of the cylinder. In this way, the average velocity of the electron stream can here be made to differ from the axial wave velocity in the electric circuit.

In Fig. 4D, there is shown an arrangement in which the axial wave velocity is modified by changes in the dielectric surrounding a particular section. To this end, dielectric 64 is added in the intermediate region 62 between the preliminary section 61 and the main section 63 in the helix circuit 60 to slow the velocity of wave propagation therethrough.

In addition to helix-type circuits, another common class of slow wave circuits is composed of wave-guiding structures generally known as of the filter type. Fig. 5 shows, in schematic form, a traveling wave tube 300 which employs a filter type circuit. An electron stream is projected from an electron gun 311 at one end of the tube to a collector electrode 312 at the opposite end of the tube. An electromagnetic wave is supplied for coupling to the electron stream by means of a wave-guiding circuit 313 which comprises a conductor having a series of lateral slots along the path of the stream. Wave energy is supplied as an input at one end of the circuit and derived for utilization at the opposite end. In operation this tube acts in the manner of a helix-type traveling wave tube. A more detailed explanation of the use of filter type circuits in traveling wave tubes may be found in the first-mentioned Pierce application. Also for the use of filter type circuits in magnetron amplifiers reference is made to the later-mentioned Pierce application.

It is well known, however, that such filter type tubes are merely modifications of the helix-type counterpart in which the helix slow wave circuit has been replaced by another form of slow wave structure. The techniques described above with reference to helix-type circuits for setting up a combination noise wave in accordance with the invention have their counterparts in the filter type circuits.

In Figs. 6A through 6D, there are shown illustrative arrangements for cancellation adapted to one typical circuit of the filter type. This particular circuit is a waveguiding structure made up of a conductor 70 having a series of lateral slots 77 of the kind shown in the tube of Fig. 5. With such a circuit, one expedient for changing the wave velocity in the direction of the electron 12 stream 'm a particular section, to make possiblethe practice of the invention, is to vary the geometry. In the circuit shown in Fig. 6A, the spacings between slots in the intermediate cancellation section 72 between the prelirninary and main sections 71 and 73 is varied to achieve the desired effect.

In the arrangement of Fig. 6B, cumulative interaction is inhibited by displacing the cancellation section 82 between the preliminary section 81 and main section 82 to limit coupling with the electron stream.

In the arrangement of Fig. 6D, the cumulative interaction is inhibited by varying the velocity of the electron stream in the region of noise cancellation. To this end, the cancellation section 92 of the electric circuit 90 is insulated from the preliminary and main sections 91 and 93, respectively, by insulating strip 94. Additionally, it is operated at a direct-current potential different from that of thc remainder of the circuit by means of source 95, thereby providing a different accelerating voltage for the electron stream within the cancellation section, whereby a new average velocity results.

Fig. 6C shows another arrangement for varying the wave propagation velocity. In this instance, the slots 97- in the cancellation section 102 between the preliminary and main sections 101 and 103, respectively, are filled with a dielectric to slow the wave velocity therethrough.

In all of the foregoing embodiments it will be readily apparent to one skilled in the art that cancellation is achieved by a variation in the electrical length of the wave propagation circuit in the cancellation section relative to the electrical length of the electron stream in the cancellation section by an amount sufficient to bring about a phase shift of approximately between the first induced noise wave in the wave propagation circuit and the noise wave induced in the rnain section.

It should be apparent at this point that the above-described arrangements are merely a few of those available. Numerous other arrangements can be devised by one skilled in the art Without departing from the spirit and scope of the invention.

What is claimed is:

l. In a device which utilizes the cumulative interaction between an electron stream and electromagnetic waves to secure gain, a source supplying an electron stream characterized by noise uctuations about an average velocity, and a continuous wave propagation circuit having a preliminary section positioned in the path of said electron stream and having a retardation characteristic for slowing the velocity in the direction of the electron stream of waves traveling therethrough to substantially the average velocity of the electron stream thereby inducing a first growing noise wave in said section which is in cumulative interaction with the electron stream, signal input means at the upstream end of said section for introducing signal waves on to said section for interaction with the electron stream, said wave propagation circuit further having a main section positioned in the path of the electron stream downstream of said preliminary section and having a retardation characteristic for slowing the velocity in the direction of the electron stream of waves traveling therethrough to substantially the average velocity of the electron stream thereby inducing a second noise wave which is in cumulative interaction with the electron stream, signal output means at the downstream end of said main section, said wave propagation circuit further having an intermediate section between said preliminary and said main sections defining a region of substantial noninteraction between the electron stream and waves traveling along said section, the electrical length of the noninteraction region relative to noise uctuations on said electron stream differing from the electrical length of the section relative to the growing noise wave on said section such that at the main section the first noise wave includes a mode of propagation which is an increasing wave equal in magnitude and opposite in phase'to theA Y i3- increasing. wave which. is a `inode of 'propagation of the second noisewave.

2.. A device according. to claim 1` in which-the. intermediate wave circuit section is. positioned so that the electric fields` in the. direction. ofV electron how. ofA waves. propagating. therethrough.` are substantially, negligible alongthe. path ofthe electron. stream..

3.,A.device. according. to claim 1. in which the inter.- mediate wave` circuit. section is: adapted for providing a. wavepropagation. of: velocity of waves. traveling therealong substantially. different. from.. the. average, velocity, of. the electron. stream. therealong.

4*.. A device. accordingto claim 1. which. inclndesvoltagegsupply means for.. changing the. average velocity'orffthe4 stream along. the.l intermediate wavecircuit. section..

5. In an electrondischargedevice. utilizing.` the inter.- actionbetween.anelectron stream? and an electromagnetic wave,. in combination. an. electron stream source and4 a. collector defining av path of electron how, saidA stream: being. characterized by. noise fluctuations .about its4 average. velocity, a. continuous wavepropagation circuit,` signal.` input means and signal output means connected to the upstream and. downstream. ends respectively of said circuit, said' circuit having a rst section adjacent' its upstream end defining;an:interaction:region with said stream fori inducing a rst growing noise-wave on said first section, a second section located downstream of; said first section. and defining an interaction. region wit-hsaid stream for inducing a noise wave on said second section, and means. for canceling the noise wave induced` on` said second section comprising a third. section between said first and second sections defining a region of substantial noninteraction: with said stream, s aid. third section being adaptedtoshift the phase relationship ofthe noise. wave induced onsaid first section andthe noise liuctuations in stream.` Y d 6j. Iman electron discharge device, the. combination as claimed in claim wherein the velocity of the noise waves propagated? inrsaidf third'` sectionA differs from the velocitylv of the electrons in said stream.

7-`.. In. anel'ectron discharge device, thecombination. as claiined in claim 5, iii further Acombination with voltage supply means for projecting the electron stream past said third section at a velocity which differs from the velocity of said stream as it traverses said first and second sections.

8. In an electron discharge device, the combination as claimed in claim 5, wherein the velocity of propagation characteristic of said third section of said rwave propagation circuit differs from the velocity of propagation of said first and second sections.

9. In an electron discharge device, the combination as claimed in claim 5, wherein said first and second sections are adjacent said electron stream and said third section is displaced from the path of said stream.

10. An electron discharge device comprising an envelope, an electron stream source and a collector for said stream defining a path of flow within said envelope, said stream being characterized by noise fluctuations about its average velocity, a continuous wave propagation circuit within said envelope adjacent said path of flow over at least a portion of its length, signal input means for launching a wave on said wave propagation circuit, signal output means at the downstream end of said wave propagation circuit, said wave propagation circuit having a first section adjacent the upstream end thereof defining an interaction region with said stream for inducing a first growing noise wave on said first section, a

second section downstream of said first section defining an interaction region with said stream for inducing a second noise wave on said second section, and means for canceling the noise wave induced on said second section comprising a third section beween said first and second sections, said third section defining a drift region of substantial noninteraction between the waves propagating therealong and said stream, the electrical length of saidf' drift region relative to the waves propagating along. said.

path, means coupled to said path intermediate. said gun,

and'` saidV input coupling to derive a beam noise voltage, and a signal` path including only passive elements and none. other between saidintermediate means and said input coupling to. apply. noise. voltage to said input coupling, the. path. length diiferences'between said signal path and said beam path from the means coupling. andl the input coupling being selected to provide at least some compensation by signals substantially in phase opposition at saidoperating frequency for signal to noise ratio at the output'.

1121. The combination comprising an electronk beam tube for signals at a.. predetermined operating frequency having an electron gun to produce a beam of electrons along apath,V an input.r coupling to. said tube at a signal input couplingV region along theA beam path, an output coupling to said tube at a region' along said beam path more remote from. said gun than said input couplingA region,` means between said gun andlsaid input coupling region tof derive. a beam noise voltage, and a signal. path including only passive elements to apply saidnoise voltage at said input voltage region, saidsignal.` path being otherwise decoupled from the beam path, the path length `difference between said signal path and' saidV beam path from said' noise voltage deriving means'to said: input region beingV a selected difference to provide signals substantially in.- phase opposition at said operating frequency wherebyv an improvement iny signal to noise ratio at the output is secured in tube operation at the operating frequency.

1.3.. The.` combination claimed in claim 12, said means to derive a beam noise voltage including a travelling wave helix having` a voltage wave velocity substantiallyY equal to. the velocity of said"V electron beam adjacent to and in signal coupling relation with said beam path.

14. The combination claimed in claim l2, said tube including a travelling wave helix between said input and output couplings adjacent to and in coupling relation with said beam path to provide signal amplification.

15. The combination claimed in claim l2, said signal path including a helix adjacent the beam path but not coupled thereto, having a voltage Wave velocity at a selected operating frequency substantially different from the beam velocity and intermediate said first mentioned helix and said input coupling.

16. The combination claimed in claim 13, further comprising a drift tube through which the beam path passes and intermediate said helix and said input coupling region.

17. The combination claimed in claim l2, said means comprising a helix adjacent to and in coupling relation with said lbeam path, and positioned intermediate said gun and said linput coupling region, said signal path comprising a further helix adjacent said beam but in noncoupl-ing relation thereto and having at least a portion of substantially difieren-t pitch from that of said first helix, said further helix being positioned intermediate said first 4helix and said input coupling region.

18. The combination claimed in claim l2, further comprising a drift tube through which the beam path passes and intermediate said gun and said input coupling region.

19. The combination comprising an amplifier having means to provide a beam of electrons along a path, beam velocity modulating means including an input coupling to the beam path and an output coupling to the beam path, whereby signals of a predetermined operating frequency applied to said input coupling may be amplified and made available Iat said output coupling, means between said beam providing means and said input couplingto derive a noise voltage from said beam, a passi-ve signal path to 'feed said noise voltage forward to said input coupling and `otherwise decoupled from said beam path, the path lengths from the noise voltage deriving means to said input coupling being related to provide at said input coupling noise signals substantially in phase opposition at said operating frequency from said signal path for beam noise uctuation compensation.

20. An electron beam device comprising: electron gun means for producing an electron beam along a path and containing noise uctuations; input means, coupled to said path, for modulating said beam in accordance with an input signal at a predetermined operating frequency; means coupled to said path between said electron gun means and said input means, for extracting a noise voltage from said beam; and signal transmission means, coupled between said voltage extracting means and said input means, for applying said noise voltage to said beam at said input means substantially 180 out of phase at said operating frequency with the noise uctuations present in said beam at that point, whereby the effect of said noise fluctuations on the operation of said device is minirnized.

21. An electron beam velocity modulation device for operation at a predetermined frequency comprising: electron gun means for producing an electron beam along a path and containing noise fluctuations; input means, coupled to said path, for velocity modulating said beam in accordance with an input signal of said frequency; output means coupled to said path beyond said input means; means, coupled to said path between said electron gun means and said input means, for extracting a noise voltage from said beam; and signal transmission means, coupled between Said voltage extracting means and said input means, for applying said noise voltage to said beam at said input means substantially in phase opposition at said frequency with the noise iluctuations present in said beam at said input means, whereby the effect of said noise uctuations on the operation of said device is minimized.

22. A device as in claim 21, wherein all of the elements recited are contained within an evacuated envelope.

23. In an electron discharge device utilizing the interv.

action between an electron stream and an electromagneticwave, in combination, an electron stream source and a collector `defining a path of flow for the electron stream, a continuous circuit extending along the path of iiow for a major portion of the length thereof for propagating electromagnetic waves adjacent the path of ow, said*l on said section are in coupling relationship with said elec tron beam, said first and second helix sections having substantially the same helix diameter, and an intermediate section between said rst and second sections having:

the same helix diameter as said irst and second sections but having `a helix pitch differing from those of the first and second sections such that electromagnetic waves on said section are decoupled from said electron beam.

References Cited in the rile of this patent UNITED STATES PATENTS 2,494,721 Robertson Jan. 17, 1950 2,516,944 Barnet-t Aug. 1, 1950 2,541,843 Tiley Feb. 13, 1951 2,575,383 Field Nov. 20, 1951 2,578,434 Lindenblad Dec. 11, 1951y 2,584,597 Landauer Feb. 5, 1952 2,595,698 Peter May 6, 1952 2,611,101 Wallauschek Sept. 15, 1952 2,616,990 Knol et al. Nov. 4, 1952 2,720,609 Bruck et al Oct. 11, 1955 2,720,610 Kazan Oct. 11, 1955 2,767,259 Peter Oct. 16, 1956 FOREIGN PATENTS 934,220 France Ian. 7, 1948I 969,886 France May 31, 1950 

